1. Technical Field
The present disclosure relates to devices for bone fusion and, more particularly, to a support system for intervertebral fusion.
2. Background of Related Art
Clinicians throughout the developed world recognize the management of low back pain as a widespread problem. Almost three quarters of the U.S. population has at one time experienced low back pain, and about 4% of Americans require surgical intervention in their lifetime, some undergoing multiple procedures. Almost 700,000 spine procedures are performed each year in the United States, and the total cost incurred by back pain and treatment for it exceeds $50 billion per year. Back problems account for almost 30% of workers' compensation claims in the United States. As the population ages, the affected group is growing at about 20% a year.
The number of support systems available for invertebral fusion has grown significantly in the last decade. Cages, inserts, supports, and other devices are commonly implanted between a pair of vertebrae of the spine in order to provide support to the vertebrae and for eventually promoting fusion between the vertebrae. Cages are generally of two types which are rectangular in cross-section or circular in cross-section. Normally, the cages will have windows extending between the top and bottom thereof to allow bone to grow through and fuse together between the vertebrae. Also, the interior of the cage is often packed with bone or other matrix that encourages the growth of bone into the cage and between the two vertebrae and, therefore, a subsequent fusing therebetween.
The shape and insertion method of these support systems vary considerably, with a few even accommodating for some degree of lordosis. Most of the cages are metal, though some are manufactured of a polymer such as polyetheretherketone (PEEK) or other suitable polymers as are known in the art, which is sometimes reinforced with carbon fibers. All the support systems available commercially today have a fixed configuration. Therefore, they are inserted into the body in the same shape as their final form. This fixed configuration of the support systems is a substantial factor in determining the size of the insertion port that is generally at least the same size as the installed support system. Since the vertebral bodies are concave, this requires either a large distraction or the carving of a large access port through the periphery of the vertebrae in order to place the bulky support system at the core of the interbody space. Both of these methods contribute to increased tissue trauma, either to ligaments and musculature in the former case, or to cartilage and vertebrae in the latter. Damage to the ligaments and musculature results in greater postoperative discomfort and a longer healing time, while damage to the vertebral body may cause the implant to fail through subsidence or dislocation.
The need for minimally invasive surgery for spinal procedures has been noted for a number of years. Minimally invasive surgery for implanting traditional prostheses has been shown to reduce intraoperative time while minimizing scarring and postoperative discomfort. These procedures carry with them a unique set of challenges and potential complications, often stemming from the complexity of the method required to implant the device.
Several devices have already been proposed for performing spinal fusion surgery using a procedure that is less invasive than conventional procedures. Some of these devices rely on several separate pieces being placed and assembled in the invertebral space. The others are inserted in a collapsed form and then expanded in the direction of load bearing. Although inserted in a less invasive manner than traditional support systems, both these types of device require considerably wide lateral access to the disc space in order to insert a support system with sufficient surface area to minimize subsidence. Concerns are also raised regarding the mechanical integrity of the devices, essentially whether they will re-collapse in situ.